Fix mismatch of connection ID between SignalR C++ client and hub

[wegylexy]

Summary of the changes

• Append negotiated connection ID to connection URL

Addresses #6980

[BrennanConroy]

Thanks for fixing this!

Would it be possible for you to add a test or two?

[wegylexy]

I lack experience in writing automated tests for client. It'd require a method in the hub to return the actual connection ID so the client can compare, and it needs a server running to test the client.

[BrennanConroy]

We currently only have unit tests for the C++ client. You could try it out if you'd like by looking at some of the current tests and copying one that's similar to the functionality we want to test. https://github.com/aspnet/AspNetCore/blob/master/src/SignalR/clients/cpp/test/signalrclienttests/connection_impl_tests.cpp#L53

Or I can do it later if you'd like 😄

[wegylexy]

I'll let you do it.

[BrennanConroy]

Thanks for the PR!